1. Field of the Invention
The present invention relates to an engine driven work machine that is driven by an engine to generate an output of a desired form and, more particularly, to an apparatus that appropriately controls cooling of the engine to form a desired output.
2. Related Art
Examples of an engine driven work machine, that is, a work machine using an engine as a drive source include for example a generator, a welding machine, and the like. These are used in urban areas and the like and work day and night, which necessitates provision of anti-noise measures.
There is an engine cooling apparatus in which an engine, a work machine, and other auxiliary machines, and the like are mounted on a common frame and housed in a sound proof case and the engine is cooled by an electric fan provided in the sound proof case (see Japanese Patent Application Laid-Open No. 2001-020740).
There is also an engine cooling apparatus in which, in order to improve engine cooling efficiency, a circuit for generating a voltage signal having frequency-voltage characteristics is incorporated in an automatic voltage regulator to operate an electric fan at the time of rated operation and idling operation (see Japanese Patent Application Laid-Open No. 2001-020741).
Engine cooling apparatuses including electric fans are classified into three types as shown in FIG. 5. There are two types that do not use an inverter (FIGS. 5A and 5B) and one type that uses an inverter (FIG. 5C). In the engine cooling apparatuses that do not use an inverter, an electric fan M is operated at a fixed number of revolutions whether electric power is supplied from a generator G together with an external load L or supplied from a battery B separately from the external load L (FIGS. 5A and 5B). When electric power is supplied from the generator G (FIG. 5A), low-speed operation sufficient for maintaining rotation of the electric fan M is performed at the time of idling of the engine E.
On the other hand, in the engine cooling apparatus that uses an inverter (FIG. 5C), an output of an inverter unit IU can be switched to 50 Hz and 60 Hz such that the engine cooling apparatus can be used throughout Japan. However, since the engine cooling apparatus is designed on the basis of 50 Hz at which an amount of cooling wind is small due to low rotational speed of the electric fan and there is no allowance in continuous operating conditions, it is inevitable that the engine cooling apparatus has allowance when the engine cooling apparatus is used at 60 Hz. The inverter unit IU includes a converter CV, an inverter IV, and a control unit CC.